基于水平分置线性双阵列的超声全聚焦成像方法在粗晶材料检测中的应用

针对粗晶材料超声检测信噪比低的问题,提出了一种水平分置线性双阵列超声成像方法。将两个线阵超声换能器沿直线水平分置在待检区域表面两侧,用收发分离的信号采集模式,一侧激发,另一侧记录各通道数据,进行聚焦成像。相比单阵列和同位置双线阵检测,文中的方法有效地减少了背向散射信号对缺陷信号的干扰,提高了成像信噪比。在粗晶铜质试块上的成像实验结果表明,当缺陷距离阵列较近时,文中的方法优于单阵列和同位置双线阵方法,成像信噪比提高约5～10 dB;当缺陷距离阵列较远时,单阵列模式和同位置双线阵检测方法失效,但文中的方法依然可以识别缺陷。文中的研究为粗晶材料的超声检测提供了一种可行的方案。     

立体微型器件的微制造技术及其在微机电系统(MEMS)的应用

综述了近年来与微型机电系统（MEMS）相关的材料微制造和微加工技术的最新研究进展.重点介绍了如何利用硅晶片作为微型模具来制备压电陶瓷和热电材料的微型柱状阵列结构和反应烧结碳化硅微型转子等微制造技术,并展望了材料微制造技术在研制微型医疗器件和微型移动能源方面的应用前景.     

Directed Molecular Collection by E‐Jet Printed Microscale Chemical Potential Wells in Hydrogel Films

A facile approach to locally concentrate analytes of interest will significantly enhance miniaturized, integrated chemical‐analysis systems. Here, the directed analyte transport and concentration using ≈200 µm‐diameter E‐jet printed chemical potential wells in a polyacrylamide hydrogel is demonstrated. Using a cationic well as the model system, anionic analytes are accumulated into a microscale area with a local concentration enhancement of >50‐fold relative to the surrounding area. By downscaling the diameter of the chemical potential well from a few millimeters to 100s of micrometers, it is found, using both fluorescence and Raman microscopy, that the molecular collection capacity of the well is greatly improved. Additionally, it is shown that molecules can be simultaneously transported and concentrated to arrays of microscale regions using an array of microscale chemical potential wells. This approach enhances many‐fold the limit of detection, enables the formation of microscale potential well arrays with a variety of chemical properties, and provides a novel microscale molecular manipulation technique as an alternative to traditional microfluidic‐based systems.     

Thinning and weighting of large planar arrays by simulated annealing

Two-dimensional arrays offer the potential for producing three-dimensional acoustic imaging. The major problem is the complexity arising from the large number of elements in such arrays. In this paper, a synthesis method is proposed that is aimed at designing an aperiodic sparse two-dimensional array to be used with a conventional beam-former. The stochastic algorithm of simulated annealing has been utilized to minimize the number of elements necessary to produce a spatial response that meets given requirements. The proposed method is highly innovative, as it can design very large arrays, optimize both positions and weight coefficients, synthesize asymmetric arrays, and generate array configurations that are valid for every steering direction. Several results are presented, showing notable improvements in the array characteristics and performances over those reported in the literature.     

Effective elastic properties of solids with irregularly shaped inclusions

A unit rectangular cell is usually cut out from a medium for investigating fracture mechanism and elastic properties of the medium containing an array of irregularly shaped inclusions. It is desirable to clarify the geometrical parameters controlling the elastic properties of heterogeneous materials because they are usually embedded with randomly distributed particulate. The stress and strain relationship of the rectangular cell is obtained by an ad hoc hybrid-stress finite element method. By matching the boundary condition requirements, the effective elastic properties of composite materials are then calculated, and the effect of shape and arrangement of inclusions on the effective elastic properties is subsequently considered by the application of the ad hoc hybrid-stress finite element method through examining three types of rectangular cell models assuming rectangular arrays of rectangular or diamond inclusions. It is found that the area fraction (the ratio of the inclusion area over the rectangular cell area) is one dominant parameter controlling the effective elastic properties.     

Elastic membranes of close-packed nanoparticle arrays

Nanoparticle superlattices are hybrid materials composed of close-packed inorganic particles separated by short organic spacers. Most work so far has concentrated on the unique electronic, optical and magnetic behaviour of these systems. Here, we demonstrate that they also possess remarkable mechanical properties. We focus on two-dimensional arrays of close-packed nanoparticles and show that they can be stretched across micrometre-size holes. The resulting free-standing monolayer membranes extend over hundreds of particle diameters without crosslinking of the ligands or further embedding in polymer. To characterize the membranes we measured elastic properties with force microscopy and determined the array structure using transmission electron microscopy. For dodecanethiol-ligated 6-nm-diameter gold nanocrystal monolayers, we find a Young's modulus of the order of several GPa. This remarkable strength is coupled with high flexibility, enabling the membranes to bend easily while draping over edges. The arrays remain intact and able to withstand tensile stresses up to temperatures around 370 K. The purely elastic response of these ultrathin membranes, coupled with exceptional robustness and resilience at high temperatures should make them excellent candidates for a wide range of sensor applications.     

Grid indentation analysis of composite microstructure and mechanics: Principles and validation

Several composites comprise material phases that cannot be recapitulated ex situ, including calcium silicate hydrates in cementitous materials, hydroxyapatite in bone, and clay agglomerates in geomaterials. This requirement for in situ synthesis and characterization of chemically complex phases obviates conventional mechanical testing of large specimens representative of these material components. Current advances in experimental micro and nanomechanics have afforded new opportunities to explore and understand the effect of thermochemical environments on the microstructural and mechanical characteristics of naturally occurring material composites. Here, we propose a straightforward application of instrumented indentation to extract the in situ elastic properties of individual components and to image the connectivity among these phases in composites. This approach relies on a large array of nano to microscale contact experiments and the statistical analysis of the resulting data. Provided that the maximum indentation depth is chosen carefully, this method has the potential of extracting elastic properties of the indented phase which are minimally affected by the surrounding medium. An estimate of the limiting indentation depth is provided by asssuming a layered, thin film geometry. The proposed methodology is tested on a “model” composite material, a titanium-titanium monoboride (Ti–TiB) of various volumetric proportions. The elastic properties, volume fractions, and morphological arrangement of the two phases are recovered. These results demonstrate the information required for any micromechanical model that would predict composition-based mechanical performance of a given composite material.     

Modeling of smart composites on account of actuation,thermal conductivity and hygroscopic absorption

The asymptotic homogenization models for smart composite materials are derived and effective elastic, actuation, thermal expansion and hygroscopic expansion coefficients for smart structures are obtained. The actuation coefficients characterize the intrinsic transducer nature of active smart materials that can be used to induce strains and stresses in a coordinated fashion. Examples of such actuators employed with smart composite material systems are derived from piezoelectric, magnetostrictive, and some other materials. The pertinent mathematical framework is that of asymptotic homogenization. The objective is to transform a general anisotropic composite material with a regular array of reinforcements and/or actuators into a simpler one that is characterized by some effective coefficients; it is implicit, of course, that the physical problem based on these homogenized coefficients should give predictions differing as little as possible from those of the original problem. The effectiveness of the derived models is illustrated by means of two- and three-dimensional examples.     

Fabrication of precisely controlled silicon wire and cone arrays by electrochemical etching

There is an exponentially growing need for well-oriented, vertical silicon nano/micro-structure arrays, particularly in high-density integrated electronic devices. Here, we demonstrate that precisely controlled vertical arrays of silicon wires and cones can be fabricated by a combined treatment strategy of electrochemical and chemical etchings. First, a periodically ordered array of silicon wires was readily fabricated at microscale by simple electrochemical etching in which the current density played a critical role in determining the wire diameter and interspacing. The microstructures fabricated by electrochemical etching were more precisely tuned by further chemical etching, thereby transforming into cone arrays with extremely sharp tips where the cone height was controlled by the etching time. This approach could have broad utility in many electronics requiring miniaturization and high-density integration such as field emitters, photovoltaic and thermoelectric devices.     

Ultrasonic arrays for monitoring cracks in an industrial plant at high temperatures

A piezoelectric linear array structure has been designed to operate at temperatures up to 400 degrees C for nondestructive testing of steel components of a hot industrial plant. It is intended that these arrays be fixed permanently to the test subject so that known defects can be monitored by comparing measurements taken over a period of time without needing to shut down the plant. The arrays are used in pairs: the transmitter is a phased array producing a variable angle steered beam, and a second array is used for receiving. The defect can be identified from a series of scans collected from individual elements of the second array. A simple monolithic array structure was used, based on a single crystal of lithium niobate and operating in the frequency range 3 to 5 MHz. Prototype devices have 64 elements on a 0.5 mm pitch. Simulated defects in steel blocks have been scanned at high temperatures to illustrate the arrays' capability for nondestructive testing. The results suggest an accuracy better than 1 mm in finding the location of crack tips.     

Effective spring stiffness for a planar periodic array of collinear cracks at an interface between two dissimilar isotropic materials

Explicit analytical expressions are obtained for the longitudinal and transverse effective spring stiffnesses of a planar periodic array of collinear cracks at the interface between two dissimilar isotropic materials; they are shown to be identical in a general case of elastic dissimilarity (the well-known open interface crack model is employed for the solution). Since the interfacial spring stiffness can be experimentally determined from ultrasound reflection and transmission analysis, the proposed expressions can be useful in estimating the percentage of disbond area between two dissimilar materials, which is directly related to the residual strength of the interface. The effects of elastic dissimilarity, crack density and crack interaction on the effective spring stiffness are clearly represented in the solution. It is shown that in general the crack interaction weakly depends on material dissimilarity and, for most practical cases, the crack interaction is nearly the same as that for crack arrays between identical solids. This allows approximate factorization of the effective spring stiffness for an array of cracks between dissimilar materials in terms of an elastic dissimilarity factor and two factors obtained for cracks in a homogeneous material: the effective spring stiffness for non-interacting (independent) cracks and the crack interaction factor. In order to avoid the effect of the crack surface interpenetration zones on the effective spring stiffness, the range of the tensile to transverse load ratios is obtained under the assumption of small-scale contact conditions. Since real cracks are often slightly open (due to prior loading history and plastic deformation), it is demonstrated that for ultrasound applications the results obtained are valid for most practical cases of small interfacial cracks as long as the mid-crack opening normalized by the crack length is at least in the order of 10⁻⁵.     

Recent attempts to design new super- and ultrahard solids leads to nano-sized and nano-structured materials and coatings

A brief overview of recent attempts to design new super- and ultrahard materials, which are based on the assumption that materials with high elastic moduli should be super- or ultrahard, is presented in order to show that meeting this condition is not sufficient. Instead, electronic and structural stability upon a finite, relatively large shear strain at atomic level is necessary to avoid structural transformations to softer phases or even a collapse of the structure. We discuss several examples where very high hardness of > 70 GPa has been obtained due to the nano-sized and nano-structured effects. Superhard nano-sized and/or nano-structured ("nanocomposites") materials can be prepared either by limited diffusion or by spinodal phase segregation during their synthesis. The advantages of the latter mentioned approach is the formation of a stable nanostructure with strong interfaces, that avoids grain boundary shear and concomitant softening when the crystallite size decreases below about 10-20 nm. In such a way, hardness enhancement by a factor of 4 to 5 has been achieved. We shall show that nc-TiN/a-Si3N4 nanocomposites can achieve hardness in excess of 100 GPa when properly designed, and prepared with low density of flaws and impurities. The paper finishes with a short overview of industrial applications of the nanocomposites as wear protection coatings on tools for machining.     

A monolithic array of three-dimensional ion traps fabricated with conventional semiconductor technology

The coherent control of quantum-entangled states of trapped ions has led to significant advances in quantum information, quantum simulation, quantum metrology and laboratory tests of quantum mechanics and relativity. All of the basic requirements for processing quantum information with arrays of ion-based quantum bits (qubits) have been proven in principle. However, so far, no more than 14 ion-based qubits have been entangled with the ion-trap approach, so there is a clear need for arrays of ion traps that can handle a much larger number of qubits. Traps consisting of a two-dimensional electrode array have undergone significant development, but three-dimensional trap geometries can create a superior confining potential. However, existing three-dimensional approaches, as used in the most advanced experiments with trap arrays, cannot be scaled up to handle greatly increased numbers of ions. Here, we report a monolithic three-dimensional ion microtrap array etched from a silica-on-silicon wafer using conventional semiconductor fabrication technology. We have confined individual (88)Sr(+) ions and strings of up to 14 ions in a single segment of the array. We have measured motional frequencies, ion heating rates and storage times. Our results demonstrate that it should be possible to handle several tens of ion-based qubits with this approach.     

Biologically inspired structural diagnostics through beamforming with phased transducer arrays

This paper discusses research in the use of biologically inspired spatial phased transducer arrays for the nondestructive evaluation of homogeneous and heterogeneous structural components. It is shown that beamforming, which is used by orb web spiders to locate their prey in a network of web fibers, can be achieved by applying weights and time delays to the tapped signals from a transducer array in a narrow frequency band to obtain desired directional sensitivities and optimal array gains. The resulting spatio-temporal filters are then used to detect, locate and quantify structural damage. The theory of beamsteering and beamforming for processing propagating wave data in damaged elastic media is discussed. Experimental results for homogeneous and heterogeneous plates are given to verify the theoretical discussions. Design considerations for the phased arrays are examined as are the benefits of nonlinear array geometries for better spatial coverage. The advantage of using adaptive over conventional beamforming is demonstrated with a Frost Constraint adaptive technique.     

Influence of parallelogram cells in the axial behaviour of fibrous composite

Effective longitudinal shear moduli closed-form analytical expressions of two-phase fibrous periodic composites are obtained by means of the asymptotic homogenization method (AHM) for a parallelogram array of circular cylinders. This work is an extension of previous reported results, where elastic, piezoelectric and magneto-electro-elastic composites for square and hexagonal arrays with perfect contact were considered. The constituents exhibit transversely isotropic properties. A doubly period-parallelogram array of cylindrical inclusions under longitudinal shear is studied. The behaviour of the anisotropic shear elastic coefficients is studied for several cell geometry arrays. Numerical examples and comparisons with other theoretical results demonstrate that the present model is efficient for the analysis of composites in which the periodic cell is rectangular, rhombic or a parallelogram. The effect of the arrangement of the cells on the shear effective property is discussed. The present method can provide benchmark results for other numerical and approximate methods.     

Phase aberration correction on two-dimensional conformal arrays

Two-dimensional conformal arrays are proposed to enhance low contrast lesion detection deep in the body. The arrays conform to the body maintaining good contact over a large area. To provide full three-dimensional focusing for two-dimensional imaging, such arrays are densely sampled in the scan direction (x) and coarsely sampled in the nonscan direction (y), i.e., the arrays are anisotropic. To illustrate reduction in slice thickness with increased array length in y, a two-dimensional array is synthesized using a one-dimensional, 128 element array with a 3.5 MHz center frequency. A mask is attached confining transmission and reception of acoustic waves to 2 mm in y. Using a mechanical scan system, the one-dimensional array is moved along y covering a 28.16 mm×20.0 mm aperture. Accordingly, the synthetic array has 128 elements in x and 10 elements in y. To correct for geometric irregularities due to array movement, a gelatin based phantom containing three-dimensional point targets is used for phase aberration correction. Results show that elevational beam quality is degraded if small geometric errors are not removed. Emulated conformality at the body surface and phase aberrations induced by spatial inhomogeneities in tissue are further imposed and shown to produce severe beam-forming artifacts. Two-dimensional phase aberration correction is applied and results indicate that the method is adequate to compensate for large phase excursions across the entire array. To fully realize the potential of large, two-dimensional, conformal arrays, proper two-dimensional phase aberration correction methods are necessary     

气相法制备纳米材料

阐述了粒子成核、粒径控制和粒子凝聚等气相合成反应的基本原理;根据前驱物的不同状态(固、液、气)对制备方法进行了分类,并对各种制备方法的特点进行了概述;气相法制备纳米材料具有粒径小、无团聚、无需后续处理的特点,已成为目前纳米制备技术研究的重点。随着科技的不断进步,新技术、新材料的不断涌现,其工业化技术也将具有非常广阔的市场前景。     

Characterization of a cross-reactive electronic nose with vapoluminescent array elements

A three-channel cross-reactive sensor array based on vapoluminescent platinum(II) double salt materials has been characterized. Two arrays were studied, one consisting of [Pt(CN-cyclododecyl)4][Pt(CN)4] (1), [(phen)Pt(CN-cyclohexyl)2][Pt(CN)4] (2), and [Pt(CN-n-tetradecyl)4][Pt-(CN)4] (3) materials, where phen = 1,10-phenanthroline, and a second array that has compound 3 replaced by the mixed double salt material [(phen)Pt(CN-cyclododecyl)Cl)]2[(phen)Pt(CN-cyclododecyl)2]2[Pt(CN)4]3 (4). Compounds 2, 3 and 4 are characterized here for the first time. Inclusion of solvent vapors into these materials often leads to dramatic shifts in their solid-state absorption and luminescence spectra. In these studies the arrays were exposed to a set of 10 test solvent vapors to determine the ability of each cross-reactive array to give reproducible vapoluminescent spectra characteristic of each solvent vapor. It was discovered that temperature programming between solvent vapor exposures greatly improved the reproducibility of the luminescence spectra obtained. A statistical analysis of three-dimensional resolution factors between pairs of solvent clusters in principal component space supported this assertion. The success of the temperature programming protocol was limited by the thermal stability and the sensitivity to low background water vapor levels of some platinum(II) double salt materials. The ability of the cross-reactive sensor array to differentiate between two different solvent vapors over a large concentration range was also investigated. Acetone and methanol were found to occupy two distinct regions of the three-dimensional principal component space. Detection limits for acetone and methanol were estimated from the principal component analysis as 75 and 6 g/m3, respectively.     

The inspection of anisotropic single-crystal components using a 2-D ultrasonic array

Single-crystal metal alloys are used extensively in the manufacture of jet engine components for their excellent mechanical properties at elevated temperatures. The inspection of these components using 2-D ultrasonic arrays potentially allows the detection of subsurface defects in threedimensions from one inspection location. Such methods are not currently suitable for the inspection of single-crystal components because the high elastic anisotropy of single-crystal materials causes directional variation in ultrasonic waves. In this paper, a model of wave propagation in anisotropic material is used to correct an ultrasonic imaging algorithm and is applied to a single-crystal test specimen. For this correctedalgorithm, the orientation of the crystal in a specimen must be known before the inspection. Using the same ultrasonic array to measure the orientation and perform the defect inspection offers the most practical solution. Therefore, potential crystallographic orientation methods using 2-D ultrasonic arrays are also developed and evaluated.     

Experimental Study of Phased Array Beam Steering Characteristics

The influence of several geometric parameters of linear phased arrays was studied. A systematic approach using an automated testing assembly was used to assess the steering performance of the array in a solid medium. In addition to calibrating the transducer with respect to its steering accuracy, this arrangement provided a detailed study of the effects of steering angle, number of elements, inter-element spacing and array aperture on the beam directivity. The experimental results show good agreement quantitatively with the predicted steering characteristics.